Data storage systems generally store data on physical media in a manner that is transparent to host computers. From the perspective of a host computer, data is stored at logical addresses located on file systems, or logical volumes. Logical volumes are typically configured to store the data required for a specific data processing application. Data storage systems map such logical addresses to addressable physical locations on storage media, such as direct access hard disks. In a typical configuration, physical locations comprise tracks on a hard disk. A track can typically store many blocks of data. System administrators frequently need to make copies of logical volumes in order to perform backups or to test and validate new applications. Data storage systems may implement the copying tasks without physically copying the data. Prior art for such implementation generally refers to the process as “instant copying.” When a logical copy is made, data only needs to be written physically when a portion of one of the copies is modified.
U.S. Pat. No. 6,779,094 to Selkirk, et al., whose disclosure is incorporated herein by reference, describes various instant copy mechanisms for copying data upon receiving a write operation to either original or copy data. Upon receiving a write operation for writing new data to a first data location, new data is written to a second data location. Multiple layers of mapping tables provide unique identification of the storage location of the data such that individual entries in the mapping tables are variable and may be self-defining.
U.S. Pat. No. 6,779,095 to Selkirk, et al., whose disclosure is incorporated herein by reference, describes the use of a plurality of layers of mapping tables for storing data. The mapping tables provide unique identification of location of the data. When the data is copied, the physical placement of the original data is described by a mapping mechanism known as the original data map. This identifies the physical storage location used to store the original data. The physical placement of the copy data is described by a mapping mechanism known as the copy data map. This identifies the physical storage location used to store the copy data.
U.S. Patent Publications 2003/0195887 and 2003/0208463 to Vishlitzky, et al., whose disclosures are incorporated herein by reference, describe a storage device containing a first storage area of a first type containing data and a second storage area of a second type containing a table of pointers to data provided in the storage area of the first type. The second storage area is a virtual storage area containing no sections of data and represents a copy of data of the first storage area at a point in time.
U.S. Pat. No. 6,820,099 to Huber, et al., whose disclosure is incorporated herein by reference, describes the use of a snapshot volume to update a primary, or “base,” logical volume. Updates are made to the snapshot volume while the base volume is still used to satisfy normal data access requests. After the updating of the snapshot is complete, the snapshot is rolled back to the base volume. During rollback, updated data are available from either the snapshot or from the base volume, and thus the updating appears to be instantaneous.
U.S. Pat. No. 6,687,718 to Gagne, et al., whose disclosure is incorporated herein by reference, describes transferring data from a data altering apparatus, such as a production data processing site, to a remote data receiving site. A data storage facility includes a first data store for recording each change in the data generated by the data altering apparatus. A register set records each change on a track-by-track basis. A second data store has first and second operating modes. During a first operating mode the second data store becomes a mirror of the first data store. During a second operating mode the second data store ceases to act as a mirror and becomes a source for a transfer of data to the data receiving site. Only information that has been altered, i.e., specific tracks that have been altered, are transferred during successive operations in the second operating mode.
U.S. Pat. No. 6,513,102 to Garrett, et al., whose disclosure is incorporated herein by reference, describes a system for transferring data from a first storage device, accessible to a first command processor, to a second storage device accessible to a second command processor but not necessarily to the first processor. In this aspect of the invention, the transfer is made internally of the storage controller rather than requiring the command processors to communicate directly with each other.
U.S. Pat. No. 6,742,138 to Gagne, et al., whose disclosure is incorporated herein by reference, describes a data recovery program that restores data in a first storage device using data from a second storage device. The program also updates the first storage device with data supplied from a host.
U.S. Pat. No. 6,574,703 to Don, et al., whose disclosure is incorporated herein by reference, describes a method for initializing an extent on a mass storage device having at least one track. The method preserves data in a track from being overwritten, and indicates that the data of the track is to be replaced. The method also associates an initialization code with the track indicating that the track is to be initialized.
U.S. Patent Publication 2003/0195864 to Vishlitzky, et al., whose disclosure is incorporated herein by reference, describes providing storage areas of a multiplicity of types that contain sections of data. Pointers are provided that are claimed to allow access or not to allow access to the data.
U.S. Pat. No. 6,839,827 to Beardsley, et al., whose disclosure is incorporated herein by reference, describes a method for mapping logical blocks to physical storage blocks. A storage controller defines the logical storage space as a sequence of logical chunks, wherein each logical chunk comprises a plurality of logical blocks in the logical storage space. The storage controller further defines a physical storage space as a sequence of physical chunks, wherein each physical chunk comprises a plurality of physical blocks in the physical storage system. The storage controller associates each logical chunk in the sequence of logical chunks defining the logical storage space with one physical chunk in the physical storage system. Further, the contiguous logical chunks are capable of being associated with non-contiguous physical chunks.
U.S. Pat. No. 6,088,764 to Shyam, et al., whose disclosure is incorporated herein by reference, describes a method for reducing space allocation failures in a computer system that utilizes direct access storage devices to store data. The method comprises the steps of determining if authorization has been given to attempt to allocate an initial space request over more than one volume, and, if so, attempting to allocate space on a plurality of volumes. If the initial space request cannot be allocated on a plurality of volumes, the initial space request is reduced by a preset percentage, an extent limit is removed and an attempt is made to allocate the reduced space request on the plurality of volumes.
U.S. Pat. No. 5,897,661 to Baranovsky, et al., whose disclosure is incorporated herein by reference, describes an apparatus providing a logical unit of undivided data storage that spans physical storage device boundaries. The apparatus manages the logical unit of undivided storage using metadata information stored on the physical storage devices. Advantageously, the apparatus replicates a minimum portion of the metadata information across all of the data storage devices and favors writing metadata only in the devices where the information is required to operate. In a preferred embodiment, a logical unit of undivided storage is created by defining a logical volume and allocating portions of available physical data storage devices thereto in order to provide a minimum logical volume size. Metadata is generated and stored on the data storage devices to provide detailed information about the portions of each data storage device that have been allocated to the logical volume.
A paper by Kang, et al., “Virtual Allocation: A Scheme for Flexible Storage Allocation,” published at the OASIS Workshop, Boston, Mass., Oct. 9-13, 2004, and available at http://ee.tamu.edu/-swkang/doc/va.pdf, is incorporated herein by reference. The paper describes physical storage allocation strategies that provide large shared areas with virtual storage for multiple file systems.
A paper by Wilson, et al., “Dynamic Storage Allocation: A survey and critical review,” published in Proceedings of the 1995 International Workshop on Memory Management, Kinrose, Scotland, UK, Sep. 27-29, 1995, Springer Verlag LNCS, and available at the website www.cs.northwestern.edu/˜pdinda/ics-f02/doc/dsa.pdf, is incorporated herein by reference. The paper covers techniques for dynamic allocation of physical storage, or heap storage.